Abstract While artificial intelligence (AI) has been promising for fusion control, its inherent black-box nature will make compliant implementation in regulatory environments a challenge. This study implements and validates a real-time AI-enabled linear and interpretable control system for successful divertor detachment control with the DIII-D lower divertor camera. Using D2 gas, we demonstrate successful feedback divertor detachment control with a mean absolute difference of 2% from the target for both detachment and reattachment. This automatic training and linear processing framework can be extended to any image-based diagnostic for future fusion reactors.

Integrated design of a snake endoscopic manipulator system for in-vessel observation of fusion reactors

Abstract The Water Cooled Lithium Lead Breeding Blanket stands out as one of the most promising designs for future fusion reactor breeding blankets. However, the significant interaction between water and Lithium-Lead, particularly triggered by an In-Box LOCA (Loss of Coolant Accident), presents a critical safety concern. This concern has spurred the scientific community to develop a sophisticated numerical analysis tool capable of simulating such a complex interaction. The SIMMER code family from JAEA has emerged as the most suitable tool for conducting safety analysis evaluations to aid in the design of the WCLL-BB at a system level. Extensive efforts have been devoted in recent years to enhancing the accuracy of simulations for such accidents. Specifically, the SIMMER code was modified by UNIPI to accurately model the chemical interaction between water and Lithium-Lead. However, further refinement of the chemical model is deemed necessary for an accurate representation of the interaction between these two fluids. This refinement involves modeling Lithium-Lead as a liquid alloy and monitoring the concentration of the chemically active element, namely Lithium. The modification has been implemented using a feature of SIMMER capable of distinguishing between Fertile and Fissile components of liquid fuel. Moreover, an initial endeavor to introduce a chemical reaction kinetic rate controlled by diffusion has been undertaken within SIMMER, drawing on the analogy between Heat Transfer and Mass Transfer. This work shows the verification of the new chemical model against the stoichiometry and the results of a SIMMER-III simulation using the new implemented diffusion model, highlighting the importance of developing the chemical kinetic for the safety evaluation of an In-Box LOCA.

The performance of conventional precipitation-strengthened copper alloys drastically degrades at temperatures exceeding 500 °C, hindering their application under extreme conditions like those in nuclear fusion reactors. Oxide dispersion–strengthened copper (ODS–Cu) alloy surmounts these constraints by incorporating thermally stable, nanoscale oxide dispersoids that simultaneously confer strengthening, microstructural stabilization, and enhanced irradiation tolerance, while preserving high thermal conductivity. This review comprehensively examines the state of the art in ODS–Cu alloy from a “processing–microstructure–property” perspective. We critically assess established and emerging fabrication routes, including internal oxidation, mechanical alloying, wet chemical synthesis, reactive spray deposition, and additive manufacturing, to evaluate their efficacy in achieving uniform dispersions of coherent/semi-coherent nano-oxides at engineering-relevant scales. The underlying strengthening mechanisms and performance trade-offs are quantitatively analyzed. The review also outlines strategies for joining and manufacturing complex components, highlights key gaps in metrology and reproducibility, and proposes a roadmap for research and standardization to accelerate industrial deployment in plasma-facing components.

Studies on energy production by proton-boron fusion reaction have gained momentum since the early 2000s, and energy systems based on this reaction have become widespread. In this study, the interaction of 2.46- and 3.76 -MeV alpha particles produced by the proton-boron fusion reaction with Li, Be, graphite, Si, and W, which are potential first-wall materials, was investigated. The radiation damage resulting from these interactions was calculated in terms of displacement per atom using SRIM/TRIM and FLUKA Monte Carlo simulation codes. In addition, the distances that alpha particles will travel while passing through the first-wall materials were calculated with SRIM/TRIM, FLUKA, and GEANT4 codes. The damage that would occur if silicon were used as the first wall was calculated to be higher than that of the other four candidates. This study clarifies that beryllium and graphite experienced less radiation damage than the other materials, particularly when compared to silicon and tungsten.

The particle exhaust system plays a pivotal role in fusion reactors and is essential for ensuring both the feasibility and sustained operation of the fusion reaction. For the successful development of such a system, density control is of great importance and some key design parameters include the neutral gas pressure and the resulting particle fluxes. This study presents a simplified conductance-based model for estimating neutral gas pressure distributions in the particle exhaust system of fusion reactors, focusing specifically on the sub-divertor region. In the proposed model, the pumping region is represented as an interconnected set of reservoirs and channels. Mass conservation and conductance relations, appropriate for all flow regimes, are applied. The model was benchmarked against complex 3D DIVGAS simulations across representative operating scenarios of the Wendelstein 7-X (W7-X) stellarator. Despite geometric simplifications, the model is capable of predicting pressure values at several key locations inside the particle exhaust area of W7-X, as well as various types of particle fluxes. The developed model is computationally efficient for large-scale parametric studies, exhibiting an average deviation of approximately 20%, which indicates reasonable predictive accuracy considering the model simplifications and the flow problem complexity. Its application may assist early-stage engineering design, pumping performance improvement, and operational planning for W7-X and other future fusion reactors.

The thermal conductivity of epoxy resin decreases sharply to approximately 0.01 W·m−1·K−1 at 4 K, significantly limiting its application in nuclear fusion engineering. To address this limitation, this study prepared epoxy composite reinforced with silver, diamond, or wollastonite at 50 vol % and 70 vol %, and systematically investigated their 4-K thermal conductivity. The results demonstrated that at 70 vol %, the silver epoxy composite achieved a thermal conductivity of 5 W·m−1·K−1, which is more than two orders of magnitude higher than that of the diamond-epoxy composite (0.05 W·m−1·K−1). At 50 vol %, the silver epoxy composite (0.12 W·m−1 ·K−1) exhibited similar thermal conductivity to the wollastonite epoxy composite (0.1 W·m−1·K−1). Increasing the silver filler from 50 to 70 vol % enhanced the thermal conductivity from 0.12 to 5 W·m−1·K−1, representing a 42-fold improvement. Through combined theoretical analysis, microstructural characterization, and finite element analysis, the following conclusions were drawn. The electron conduction–dominated fillers were the preferred choice for the cryogenic thermal conductivity epoxy composite. In the discrete composite, even the electron conduction–dominated filler could not significantly improve the cryogenic thermal conductivity of the epoxy composite; even 50 vol % silver only reached approximately 0.12 W·m−1 ·K−1. The synergistic effect between the filler type and the distribution (electron conduction–dominated filler combined with continuous filler distribution) can substantially enhance the cryogenic thermal conductivity of the epoxy composite. This work provides technical support for the design of high-performance thermal management materials for superconducting magnet cooling systems in fusion reactors.

Accelerator based fusion reactor with magnetic mirror

Vanadium alloys are highly promising as structural materials of fusion reactor blanket, owing to their excellent high-temperature strength, and good compatibility with liquid metal lithium, which functions as both a coolant and a fuel tritium breeder material. Chemical composition of V-4Cr-4Ti has been selected as the primary candidate after systematic investigations into its neutron irradiation properties. Since V and Cr do not produce long-lived radioactive isotopes emitting high-energy gamma rays even under intense neutron irradiation conditions, low-activation characteristics are primarily governed by Ti and detrimental high-activation impurities, such as Co, Cu, Fe, Mo, Nb, and Ni. Very early material recycling, such as remote recycling within ten years, and re-use even in the same fusion reactor is achievable through effective impurity removal and minimization of Ti concentration. This paper discusses the progress in and mechanisms of vanadium metal refining. Additionally, the present paper reviews recent results and current status of redesign efforts for the Cr and Ti concentration balance to identify a new high-Cr and low-Ti composition, maintaining various attractive properties of the V-4Cr-4Ti alloy.

Materials used in commercial D-T fusion reactors will be exposed to irradiation and a mixture of helium and hydrogen plasma. Modeling the microstructural evolution of such materials requires the use of large-scale molecular dynamics simulations. The focus of this study is to develop a fast EAM potential for the interactions among the three elements (W, H, and He), fitted to accurately reproduce both the ab initio formation energies and relaxation volumes of small defect clusters containing light gases within tungsten. The potential enables the study of tungsten under irradiation and in the presence of light gases. To demonstrate the utility of the potential, we construct a thermodynamically motivated model for predicting the energetics of light-gas-filled voids. The model is then validated through molecular dynamics simulations with our new potential.

Abstract The enhanced D α (EDA) H-mode features high energy confinement together with the absence of edge localized modes (ELMs) and impurity accumulation, making it highly attractive for fusion reactors. The EDA H-mode has been observed recently in the HL-3 tokamak. This regime exhibits high energy confinement ( H 98,y2 = 0.8 ~ 1.05 ), and without the occurrence of large ELMs. The EDA H-mode is achieved at a relatively high edge safety factor (q 95 = 4.5 ~ 5.7) and high plasma triangularity (δ avg = 0.5 ~ 0.6), where the upper triangularity (δ U > 0.3) is found to be essential. A distinct quasi-coherent mode (QCM) with a frequency of 20 kHz is detected in edge density and temperature fluctuations during the EDA H-mode phase. The QCM has a poloidal wavenumber of k ~ 0.4 cm -1 , a radial wavenumber of k r ~ 0.2 cm -1 , and propagates in the ion diamagnetic drift direction in the plasma frame. Bispectral analysis shows strong nonlinear interactions between the QCM and broadband turbulence in the pedestal region. By regulating the pedestal particle transport, the QCM limits the growth of the edge plasma pressure gradient, thereby maintaining an ELM-free state in EDA H-mode.

Abstract A promising approach to handle the intense plasma heat flux in the divertor region of a tokamak is the Vapour Box Divertor (VBD). Here plasma-lithium interaction creates a dense lithium vapour cloud which interacts with the incoming plasma, effectively shielding the tungsten surface beneath, therefore preventing overheating and sputtering of the tungsten and increasing the component's lifetime. Two key steps must be addressed to validate this concept: investigating plasma-Li interactions and the transport mechanism of the latter in the presence of plasma. To explore this, a Vapour Box Module (VBM) has been designed for use with the linear plasma generator Magnum-PSI. The VBM consists of a series of three cylindrical boxes, with Li being evaporated at a controlled temperature in the central box. Divertor-like plasma enters the VBM from an upstream aperture, interacts with the Li vapour cloud and exits through a downstream aperture ultimately impacting a target equipped with a calorimetry system. Optical diagnostics Thomson scattering, Filtered fast camera Imaging and Optical Emission Spectroscopy provided information on plasma parameters in terms of electron density n e , temperature T e and plasma composition before and after this interaction. A significant reduction in plasma power was observed upon the establishment of lithium vaporization determined via cooling water calorimetry and embedded thermocouples at the downstream target. This resulted in a drop of the target temperature from ~ 800 °C to ~ 350 °C (57%) at the highest applied power (11.1 MW m -2 ) and central box temperature ~ 700 °C). Lithium condensation at the side boxes of the VBM in combination with strong plasma momentum transfer effectively prevented upstream migration of lithium, while enhancing Li transport toward the target. The achievement of the two main goals of reducing plasma power and confining the Li in the VBM, are consistent with earlier published preliminary SOLPS-ITER simulations. This study shows that the presence of lithium in a vapour box divertor-like configuration can result in a strong reduction of power to the target surface, while at the same time the lithium vapour is effectively confined by the VBM, aided by the incoming plasma, preventing its escape from the VBM geometry. This represents a valuable step toward validating the feasibility of the VBD configuration in future fusion reactors.

Abstract Plasma state reconstruction methods combining measurements and physics modeling improve the estimation of physics quantities in real-time and in post-discharge analysis. We present a workflow to reconstruct the dynamic evolution of a set of internal tokamak plasma profiles with consistent equilibria, as applied in this paper for experimental data from TCV L and H-mode discharges. 
Plasma profile estimates for electron temperature T e , electron density n e and parallel current density j par are obtained by data assimilation of Thomson scattering (TS) measurements into RAPTOR modeling, using an Extended Kalman Filter (EKF). A new kinetic equilibrium reconstruction method ensures mutual consistency of free-boundary equilibrium reconstruction, core plasma profile estimates and mapping of the TS measurements to flux surface coordinates. The RAPTOR code captures the coupled dynamics of electron heat, particle and current density transport and includes a model for the onset conditions of sawtooth instabilities and the resulting profile relaxations after a sawtooth crash, enabling a realistic q profile reconstruction even in the absence of direct measurements. During phases with sawtooth instabilities, the sawtooth period and inversion radius inferred from soft X-ray measurements are in excellent agreement with RAPTOR EKF inner q profile reconstructions and the predicted sawtooth dynamics, even for transient phases. 
In addition to the plasma profiles, the EKF allows to infer unknown physics quantities such as the effective charge Z eff and the on-axis ion-to-electron temperature ratio T i0 /T e0 , as well as transport model parameters. Continuously updating the transport model parameters for electron heat and density transport, based on the available measurements, is an effective way to reduce the model-to-reality gap, as required for real-time model-based control of fusion reactor plasmas.

We assess the disorder created in lithium oxide, an important candidate material for tritium breeding in fusion nuclear reactors, by high-energy neutron bombardment. Steinhardt order parameters distinguish the different local environments of Li ions in the damaged structure, differentiating between interstitial and lattice sites. The order parameters are also used to determine the evolution of the damage with time. We estimate the time needed for healing to return to the pre-damaged structure over a range of temperatures and show that this is at a minimum at temperatures close to the working conditions of a breeding blanket.

This research proposes an innovative method that proton irradiation technology for defect control in practical engineering YBCO tapes,to improve the critical current density of YBCO high-temperature superconducting tapes in high magnetic fields.Based on the material irradiation terminal of a 4.5 MV electrostatic accelerator at Peking University, systematic irradiation experiments were conducted using 3 MeV proton beams on YBCO superconducting tapes at different fluence rates, successfully constructing high-density, low-dimensional controllable artificial pinning centers in the high superconducting tapes. This defect engineering significantly suppresses the flux creep phenomenon and enhances the pinning effect by creating low-energy pinning sites for flux lines, thereby significantly weakening the inhibitory effect of external magnetic fields on critical current (Ic). Comparative analysis of superconducting tapes before and after irradiation, including superconducting transition temperature, superconducting critical performance, and critical current density on magnetic field dependence.As the irradiation dose increases, high-density point defects (vacancies, interstitial atoms, etc.) and a small number of vacancy clusters are implanted inside the superconducting tape, resulting in a corresponding decrease in the superconducting phase. Therefore, as the dose increases, the orderliness of the superconducting phase in the superconducting tape decreases sharply, leading to a gradual widening of the superconducting transition temperature zone. By measuring the hysteresis loops of samples irradiated with different doses of protons and calculating the critical current density Jc based on the Bean model, the experimental data show that under irradiation conditions with a fluence rate of 8×10<sup>16</sup> P/cm<sup>2</sup>, the critical current of the sample under extreme operating conditions of 4.2K@6.5T achieved an 8-fold breakthrough improvement. Meanwhile, the maximum improvement factors in critical current density at 20K@5T and 30K@4T were also 5.5 times and 4.8 times, respectively. The logarithmic curve was fitted using the Jc ∝ B– α power exponent model to obtain the power parameterα values of 0.276, 0.361, and 0.397 for the variation of critical current density with magnetic field at three temperature ranges of 4.2K, 20K, and 30K, respectively. This indicates that the superconducting tape irradiated with protons will form more effective strong pinning centers at lower temperatures, reducing the dependence of the critical current density of the superconducting tape on the magnetic field.This performance breakthrough significantly enhances the application potential of high superconducting tapes in low-temperature and high magnetic fields environments, especially in frontier fields such as particle accelerators and fusion reactors, where there is an urgent demand for high-performance superconducting magnets. The study confirms that proton irradiation technology can achieve efficient optimization of critical performance through defect engineering without altering the existing preparation process of YBCO tapes, providing a highly feasible and process-compatible technical path for practical performance control of superconducting materials.

Doubly-Periodic Processing in Particle Accelerators and Fusion Reactors

Feasibility study on spray cooling for helium circulator in Fusion Reactor using the numerical simulations based on the DPM-to-VOF transition model

Magnetic confinement on fluctuating waves of heat radiations using ohmic heating around oscillatory fuel-sphere in fusion reactors: Energy dissipation model

A systematic and general nonlinear optimization strategy for integrated structural-sealing design of large and complex vacuum components in fusion reactors

Abstract Plasma Position Reflectometry (PPR) is a leading candidate to complement or replace magnetic diagnostics in DEMO and next-generation fusion devices. The concept of a multi-reflectometer PPR system is currently under development for DEMO, requiring detailed studies of reflectometer performance across different regions of the machine. This work presents the first comprehensive assessment of a multi-reflectometer PPR system using recently developed simulation and data processing automation techniques.

A system of reflectometers, located at different poloidal positions around the vessel, is modeled using the 2017 DEMO baseline scenario. The separatrix position error and signal amplitude are evaluated across various plasma and geometry configurations to assess the impact of key system properties, including reflectometer configuration, density curvature, plasma-wall reflections, scrape-off layer decay length, and turbulence-induced errors. Results indicate that while the midplane region meets the 1 cm requirement threshold, further optimization is needed for the divertor and upper poloidal regions.

The PPR system's performance is optimized by adjusting the probing direction and maximizing the average detected signal amplitude across the frequency range. Effective measurement solutions are identified in the upper poloidal and divertor regions. The robustness of the optimized system is assessed by analyzing macroscopic plasma displacements (5–15 cm) and group delay initialization. The results demonstrate that a well-configured PPR system can achieve reliable position measurements across different poloidal regions, confirming its viability for future fusion reactors.